During the summer of 2006, from her office adjacent to the White House, deputy national security adviser Meghan O'Sullivan sent President Bush a daily top secret report cataloging the escalating bloodshed and chaos in Iraq. "Violence has acquired a momentum of its own and is now self-sustaining," she wrote July 20, quoting from an intelligence assessment.

Her dire evaluation contradicted the upbeat assurances that President Bush was hearing from Gen. George W. Casey Jr., the U.S. commander in Iraq. Casey and Defense Secretary Donald H. Rumsfeld were pushing to draw down American forces and speed the transfer of responsibility to the Iraqis. Despite months of skyrocketing violence, Casey insisted that within a year, Iraq would be mostly stable, with the bulk of American combat troops headed home.

Publicly, the president claimed the United States was winning the war, and he expressed unwavering faith in Casey, saying, "It's his judgment that I rely upon." Privately, he was losing confidence in the drawdown strategy. He questioned O'Sullivan that summer with increasing urgency: "What are you hearing from people in Baghdad? What are people's daily lives like?"

"It's hell, Mr. President," she answered, determined not to mislead or lie to him.

O'Sullivan was 36, with a PhD from Oxford and a year's experience in Iraq. As the violence had escalated, she began to feel that the strategy of drawing down had become indefensible. For months, she had urged her boss, national security adviser Stephen J. Hadley, to begin a full strategy review.

That summer, with U.S. casualties eclipsing 2,500 deaths and nearly 20,000 wounded, Bush acknowledged to himself what he was not saying publicly: The war had taken a perilous turn for the worse, with 1,000 attacks a week, the equivalent of six an hour. "Underneath my hope was a sense of anxiety," Bush recalled in a May 2008 interview. The strategy was one "that everybody hoped would work. And it did not. And therefore the question is, when you're in my position: If it's not working, what do you do?"

This is the untold history of how the Bush administration wrestled with that question. Compiled from classified documents and interviews with more than 150 participants, it reveals that the administration's efforts to develop a new Iraq strategy were crippled by dissension among the president's advisers, delayed by political calculations and undermined by a widening and sometimes bitter rift in civilian-military relations.

No administration willingly puts its disagreements on display, but what happened in Washington during 2006 went beyond the usual give-and-take of government. The level of distrust became so severe that Bush eventually activated a back channel to Casey's replacement in Iraq, Gen. David H. Petraeus, circumventing the established chain of command. While the violence in Iraq skyrocketed to unnerving levels, a second front in the war raged at home, fought at the highest levels of the White House, the Pentagon, the Joint Chiefs of Staff and the State Depart ment.

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By mid-2006, Casey, a stout four-star general with wire-rim glasses, had been the commander in Iraq for two years. As American military units rotated in and out, Casey remained the one constant.

He had concluded that one big problem with the war was the president himself. Since the beginning, Casey felt, the president had viewed the war in conventional terms, repeatedly asking how many of the various enemies had been captured or killed. Casey later confided to a colleague that he had the impression that Bush reflected the "radical wing of the Republican Party that kept saying, 'Kill the bastards! Kill the bastards! And you'll succeed.' "

Casey was troubled by the thought that the president didn't understand the nature of the fight they were in. The large, heavily armed Western force was on borrowed time, he believed. The president often paid lip service to winning over the Iraqi people, but then he would lean in with greater interest and ask about raids and military operations, grilling Casey about killings and captures.